Effects of colipase on hydrolysis of monomolecular films by lipase.

In a system free of bile salts we measured lipase hydrolysis of 1,3-didecanoylglycerol films in the presence or absence of colipase at different surface pressures. The strong, but not absolutely specific protective effect of colipase, most visible at low surface pressure, can account for the higher enzyme activity in the presence of colipase. This can be understood by taking into account simultaneous penetration and surface inactivation fluxes. Using radioactively labeled lipase, we have shown for the first time in a bile salt-free system that the critical surface pressure above which lipase can no longer penetrate a 1,2-didodecanoylphosphatidylglycerol monlayer is around 23 dynes/cm. Colipase increased this critical surface pressure to 30 dynes/cm indicating that it enables lipase penetration between 23 and 30 dynes/cm. The transfer experiment showed that colipase acts by first penetrating the lipid film and then serving as an anchor for lipase into the film.